Hydraulic impactor methods and apparatus

ABSTRACT

Methods and apparatus for generating two separated fluid flows that each include direct flow components as well as alternating, out-of-phase flow components, such separated flows being transmitted into two separate cavities that have interposed between them a mass capable of periodic movement responsive to the out-of-phase alternating flows. The direct flow component is discharged from each cavity through a passageway having entrances adjacent the ends of an enlarged central portion of the mass to center the mass. In addition, a flow restriction means in a discharge port connected with the passageway maintains a selected pressure level in the system. The sizes of the cavities, the size of the mass and the differential areas of the mass produce a selected ratio of the operating frequency to the natural frequency of the system.

1451 Oct. 24, 1972 [54] HYDRAULIC IMPACTOR METHODS AND APPARATUS [72] Inventor: Edward M. Galle, Houston, Tex.

[73] Assignee: Hughes Tool Company, Houston,

Tex.

[22] Filed: April 5, 1971 [21] Appl.No.: 131,123

52] us. 01. ..60/52 1m, 60/52 R 51 Int. Cl ..Fl5b 15/18 581 Field of Search ..60/52 R, 52 HF, 52 W1 [56] References Cited UNITED STATES PATENTS 2,941,475 6/1960 Blair ..417/238 2,960,828 11/1960 Gould ..60/52 R 3,115,751 12/1963 McGee ..60/52 VM Primary Examiner-Edgar W. Geoghegan Attorney-Robert A. Felsman ABSTRACT Methods and apparatus for generating two separated fluid flows that each include direct flow components as well as alternating, out-of-phase flow components, such separated flows being transmitted into two separate cavities that have interposed between them a mass capable of periodic movement responsive to the out-of-phase alternating flows. The direct flow component is discharged from each cavity through a passageway having entrancesadjacent the ends of an enlarged central portion of the mass to center the mass. In addition, a flow restriction means in a discharge port connected with the passageway maintains a selected pressure level in the system. The sizes of the cavities, the size of the mass and the differential areas of the mass produce a selected ratio of the operating frequency to the natural frequency of the- .7 system.

..25 prsw nsfi w PATENTEUnm 24 972 SHEET 2 BF 3 T ORNE Y5 PATENTED B I97? 7 3.699.675

sum 3 or '3 HYDRAULIC IMPACTOR METHODS AND APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates in general to impactor apparatus and methods, and in particular to fluid operated impactors used for operations such as pavement demolition.

2. Description of the Prior Art There have been developed in the prior art a number of devices used to vibrate masses through utilization of out-of-phase, alternating fluid flows in separate flow channels that communicate with respective sides of a piston. One such apparatus is shown in the patent to H.

apparatus. The most significant detrimental effect of utilizing a low ratio is that high power delivery to the work piece cannot be practicably accomplished.

SUMMARY OF THE INVENTION The invention may be summarized as a method of and apparatus for impacting, utilizing the steps of generating out-of-phase, alternating fluid flows, as well as direct fluid flows in two separated fluid outputs or regions. Such flows are then transmitted to two separate cavities, which have interposed therebetween a mass or piston carried by a housing and being capable of periodic movements responsive to the out-of-phase fluid flows into the cavities. The direct flow components are discharged from the cavities, while maintaining a selected fluid pressure sufficient to prevent tionship to the operating frequency, produces in creased destructive capabilities during such operations as pavement demolition.

Another object of the invention is to provide in a hydraulic impactor a hydraulic system that utilizes a quantity of alternating fluid flow and a quantity of direct fluid flow at selected pressure levels in a manner that eliminates cavitation and maintains essentially constant fluid properties.

Another object of the invention is to provide an improved piston centering means that includes in a housing a passageway that has its ends terminating at the inner surface of the housing approximately at the extremities of an enlargedportion of the piston, and in communication with a discharge port.

Another object of the invention is to provide means for producing alternating fluid flow and direct fluid flow through utilization of apump of the wobble plate type, wherein the pistons are divided into two banks or groups, some of the pistons in each bank being associated with inlet and outlet valves to produce a direct flow component, while the other of said pistons in each bank have no outlet valve and thus produce an alternating flow, the direct flow component being used to assist in preventing cavitation and in maintaining a selected pressure level in the system in order to insure that the acoustic properties of the fluid will remain essentially constant during all portions of the operating cycle.

The above and other objects, features and advantages of the invention will become more fully apparent in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of a housing containing a hydraulically driven piston, and supporting a moil driven by the piston with periodic blows for impacting pavement or otherselected surfaces and materials.

FIG. 2 is a fragmentary side elevational view, partially schematic and in section, of apparatus of the type shown in FIG. 1.

cavitation in the system. The reciprocating mass is used to impact a moil fashioned to effectively break pavement or other selected materials. For the purpose of keeping the piston centered, a passageway in the housing with its ends terminating near the extremities of an enlarged central portion of the piston is connected with a discharge port and flow restriction means that maintains the selected pressure level in the system. Hence, the fluid flow past the edges of the enlarged central portion keeps the piston centered with respect to the housing. The size of the hydraulic cavities, the mass of the piston, and the differential area of the mass acted on by the fluid in the cavities all cooperate to form a system natural frequency such that the ratio of the operating frequency to the system natural frequency is within a selected range to produce advantageous operating characteristics.

It is, therefore, the general object of this invention to provide improved, hydraulic impactor methods and apparatus.

Another object of the invention is to provide hydra lically operated impactor apparatus having fluid filled cavities, a piston mass, and piston differential areas that cooperate to form a natural frequency, which in rela- FIG. 3 is a cross sectional view as see looking along the lines III III of FIG. 2.

FIG. 4 is a fragmentary, partially sectional side elevational view of aregion of the apparatus shown in FIG. 2.

FIG. 5 is a side elevational view, partially in section, showing the housing and piston arrangement of FIG. 2, as well as fluid flow generator means for producing outof-phase fluid flows having direct flow components as well as alternating flow components.

FIG. 6 is a fragmentary side elevational view, partially in section of bearing means used between the piston and the housing.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, the impactor apparatus per se (excluding the power means for driving the impactor) comprises a housing 11 that includes an upper housing section 13 and a lower housing section 15 secured to a central body 17 by suitable fastener means such as the socket head set screws 19, there being two input port fittings 21, 23 and a discharge port fitting 25, all being adapted for securement with suitable conduits or transmission lines.

Secured to the lower portion of the housing 11 is a moil 27 having its lower end portion 29 shaped in a manner to efficiently demolish a surface or material such as pavement concrete for example.

In FIG. is shown a fluid flow generator means for producing direct flow components and alternating flow components, such means including a conventional hydraulic motor 31 having its fluid output 33 in fluid communication through a conduit 35 with the inlet port 37 of an alternating flow hydraulic pump 39. This pump has a plurality of cylinders 41 and pistons 42 divided into two banks B and B one of which banks pumps fluid into a fluid flow output conduit 43, such flow being partially alternating and partially direct, as will become more fully apparent hereinafter. The second of said banks B is in fluid communication with another fluid output or conduit 51, and also contains fluid flow that is partially alternating and partially direct.

All of the cylinders 41, or the pistons 42 therein, contain an inlet check valve 47; whereas, only a selected portion of the cylinders in each bank contain an outlet check valve 49. More specifically, in each bank B and B there is at least one piston that has an inlet check valve 47, and the cylinder associated with this piston has an outlet check valve 49, the purpose of such arrangement being to provide the output of each bank of pistons and cylinders with a small quantity of direct fluid flow in addition to the alternating fluid flow produced by the remaining pistons and cylinders in each bank. Except for the alteration described above relative to the production of both alternating and direct flow, the pump utilized as a component of this invention may be of .the type shown in US. Pat. No. 2,941,475, issued to David T. Blair on June 21, 1960. As modified in the manner explained above, the hydraulic pump will have two out-of-phase, alternating fluid flow outputs, each output having a direct fluid flow component in addition to an alternating fluid flow component. It is only necessary to have inlet and outlet check valves in each piston and cylinder that pumps a direct flow component. The alternating flow components can be produced with a solid piston and no outlet check valve. The term out-of-phase is intended to mean a phase relationship that is as close as practicable during operation of the apparatus to a 180 phase relationship, although other phase relationships are within the scope of the invention, even though they are not as efficient as a 180 phase relationship.

Thus, the conduits 43 and 51 each have an alternating flow (AF) and a direct flow (D.F.) component and are connected respectively with inlet ports 55, 53 of the housing 11. The conduits 43 and 51 may be flexible hoses and the housing 11 may have fittings 21, 23 as shown in FIG. 1 for connection with the flexible hoses (not shown). Flow from the inlet port 53 communicates with a first fluid cavity 61, while the fluid received by the inlet port 55 communicates with a separate, second fluid cavity 63 such that an out-ofphase, alternating flow relationship is introduced into the respective cavities. The alternating flow components introduced into cavities 61, 63 during operation of the impactor are as close as practicable to being l80 out-of-phase, and reciprocate a piston 59 interposed between the cavities to periodically strike the end of the moil 27.

The D.F. components entering ports 53, 55 of the housing 11 are fed to a discharge port 67, which includes a flow restriction means 69, in this case an orifree, to maintain a selected positive average pressure in the cavities 61, 63. Two centering holes 71, 73 (see especially FIG. 4) form a portion of a centering means that here comprises a passageway 74 that has its ends terminating at the extremities of an enlarged mid-region 76 of the piston 59, such passageway leading to the discharge port 67. When the piston 59 is below its central position, centering hole 71 is opened and centering hole 73 is closed such that fluid passes from the upper or first cavity 61 through centering hole 71 and flow restriction means 69, thus reducing the average pressure in cavity 61 and tending to urge piston 59 upwardly. Similarly, the lower cavity 63 feeds flow restriction means 69 through centering hole 73 when the piston 59 is above center, which reduces the average pressure in cavity 63 and tends to urge the piston downwardly. This arrangement keeps the piston cen-' tered during operation.

An outlet port 75 from the pump 39 and the flow from discharge port 67 of the housing 11 return to a sump or reservoir 77 through a conduit 79. An additional pump 81 circulates fluid from the reservoir 77 through a conduit 83 to an input 85 of the motor 31, such motor having a drive shaft 86 that rotates the wobble plate 88 in pump 39.

With reference especially to FIG. 2, the lower housing section 15 supports on its lower and region the moil 27, which has a shoulder 89 intermediate its upper end 91 and its lower end 93 to limit axial travel of the moil in combination with an upper guide bushing 95, a spacer 97 and a lower guide bushing 99. A retainer means 101 (see especially FIG. 3) secures the bushings 95, 99 and spacer 97 within the lower housing section 15, such retainer means in this instance comprising an annular groove 103 formed in the exterior periphery of a ring 104. One or more retainer pins 105, each inserted through a drilled hole 106 essentially tangential to annular groove 103, secure the ring 104 in housing section 15.

The piston 59 has in this instance a lower portion-107 adapted to be received for reciprocation within a lower piston bearing means or bushing 109 retained by suitable means within the lower housing section 15, such means being here a retainer ring 111 secured by fasteners such as the socket head cap screws 113 against an outwardly facing shoulder 115 extending from a lower region of the bushing 109.

Formed on the interior of the bushing 109 cylindrical surface is a collector groove 1 17 (see especially FIG. 6) that communicates with a passage 119 extending through the lower bushing 109 into combination with a passage 121 leading to the discharge port 67 of the housing. Suitable seals such as the high pressure seal 123, low pressure seal and wiper ring 127 control fluid leakage from the second or lower fluid cavity 63.

The above system of sealing allows the collection of any small amount of leakage past high pressure seal 123 and returns such leakage to the sump or reservoir 77 (see FIGS. 2 and 5) from collector groove 117 via passages 119, 121, discharge port 67 and the conduit 79. The function of the low pressure seal 125 is to ensure that all leakage past high pressure seal 123 is collected in the collector groove 117 and subsequently returned to sump 77. Wiper ring 127 serves to exclude foreign material or debris from damaging low pressure seal 125. A similar sealing system is used on the upper end portion of the piston 59 except that no wiper ring is necessary since the upper end 128 of the piston is not subject to severe contamination.

Annular seals 129 and 131 are provided on the lower radial surface of the shoulder 115 of bushing 109. Seal 131 is provided to contain the higher pressure hydraulic fluid in cavity 63, and seal 129 is provided to ensure that hydraulic fluid passing through passage 119 enters passage 121, which has a radially drilled portion 130 and a sealing cap 132.

The upper portion 128 of the piston 59 is received by an upper piston bushing l33that is retained in this instance to the housing by one or more suitable fasteners 135. Such upper piston bushing has a sealing arrangement substantially similar to that previously described in discussion of the lower piston bushing.

The enlarged mid-region 76- of the piston 59 comprises an enlarged portion having a plurality of annular grooves 140 for the purpose of ensuring proper lubrication and preventing hydraulic lock. In a similar manner and for the same purpose, annular grooves 141 are formed in the interior cylindrical surface of the upper and lower piston bushings 133, 109.

The housing 11 further comprises the central body 17 adapted to receive a central bushing 145 that slidingly engages the enlarged portion 76 of the piston, such bushing being retained here by a press tit and retainer rings 147. The discharge port 67 of the housing communicates with the first, upper fluid cavity 71 through an axially extending groove or passageway 74, formed on the exterior of the central bushing 145, and the radially extending centering hole 71, as previously explained. In addition, the discharge port 67 communicates with the second or lower fluid .cavity 63 through the groove 74 and centering hole 73,- provided the piston 59 is in the centered position illustrated in FIG. 2.

As explained above, the central bushing comprises a first bearing means, while the upper and lower bushings 133, 109 comprise upper and lower, second bearing means to support the end portions of the piston. As shown, the passageway 74 is formed through the housing, the bushing 145 being a portion thereof, and having its ends terminating at the inner surface 146 of the first bearing means approximately at the extremities of the enlarged end region of the piston.

In the origination of satisfactory impactor apparatus it is necessary to consider the volume of fluid contained in cavities 61, 63, the mass of piston 59, the differential areas of the mass acted upon by the fluid in the cavities, the elasticity or springiness of the impactor members forming the boundaries of cavities 61, 63 and the compressibility of the hydraulic fluid used, in order to attain the proper and desired operation of the impactor for any given alternating flow input to inlet ports 53, 55

and for any given frequency of operation. The prior art devices which utilized alternating flow hydraulic fluid as a driving means do not appear to give consideration to the aforementioned items.

As previously stated, one of the prior art patents is the US. Pat. No 3,115,751. This patent discloses a hydraulic reciprocatory device, the purpose of which is to serve as a vibrator which as disclosed may be satisfactory for such purpose. However, such an apparatus is: disadvantageous, if not completely impracticable, as a means for producing high impact energy for a demolition tool in which a piston strikes a moil and is suddenly stopped. With a solid column of fluid between the pump and the piston in the apparatus as disclosed by McGee, and with the sudden stopping of the piston as occurs in an impactor device, the fluid pressure above the piston would rise to a very high value.

ln'an impactor tool where the piston is suddenly stopped by striking a moil or other working piece, means must be provided for ensuring that hydraulic fluid pressures do not exceed acceptable limits when such sudden stoppage of the piston occurs. Likewise, it is advantageous to provide a system which ensures that cavitation does not occur in any portion of the hydraulic system. When utilizing a direct flow and alternating flow hydraulic pump to drive an impact device, sufficient volumes of fluid must be provided between the output of the pump and the reciprocating piston of the impacttool to prevent excessive pressure rises during certain portions of the cycle.

An example of a hydraulic impactor with physical sizing and dimensioning that will produce satisfactory results under actual operating conditions is as follows:

A satisfactory alternating flow pump 39 is manufactured under the trademark Dynex by Applied Power Industries, Inc. and designated Model PF4033, but with modifications in the outlet porting and check valve arrangement as previously described. This pump has an alternating flow amplitude of 0.0429 cubic feet per second per bank when operating at 1,600 rpm shaft speed. This pump also has a direct flow output per bank of 0.005 cubic feet per second when operating at 1,600

rpm, with only one of the five cylinders per bank having both inlet and outlet check valves. The rated continuous operating pressure for this pump is 4,000 psia. The conduits or transmission lines 43, 51 which connect to the output of the alternating flow hydraulic pump are 7 A medium weight hydraulic oil (Texaco Rando Hydraulic Oil HD A) is used in the hydraulic system. A Commercial Shearing Model 25X gear motor having a gear width of 1% inch is used to drive the alternating flow hydraulic pump. This motor is driven by a hydraulic source having an output of 25 gallons per minute at 1,750 psi. Using the above components mounted on a backhoe tractor having a hydraulic pump supplying 25 gallons per minute at 1,750 psi, resulted in an effective and efficient impactor for commercial purposes.

In the above described apparatus one feature that leads to successful operation relates to the use of the flow restriction means 69 in the discharge port 67 of the housing of the hydraulic impactor. Without flow restriction means the hydraulic fluid pressure at various 7. points in the system will fall to a low level which will allow the fluid to separate, resulting in poor transfer of energy through the hydraulic fluid and the detrimental effects of cavitation. Under cavitation conditions, the tool of this invention will not operate and deliver the desired impact energy to the moil or other working tool. However, by providing a flow restriction means such as an orifice 69 in discharge port 67, the average pressure of the hydraulic fluid in cavities 61, 63 and the associated conduits or transmission lines 43, 51, including the alternating flow hydraulic pump cylinders, may be maintained at an average pressure sufficiently high to prevent cavitation. It is critical relative to optimum operation not to allow any point in the system to fall below 250 psia so that the presence of air, which almost always occurs in hydraulic fluids, will not have an effect upon the compressibility or acoustic properties of the fluid in the system. Maintaining a selected minimum fluid pressure of 250 psia at all points in the system will ensure that the acoustic properties of a commercial grade hydraulic fluid (as for example the previously identified hydraulic fluid) used in a typical hydraulic system, will be essentially constant during all portions of the operating cycle.

Another feature of the above described apparatus leading to the provision of a successful hydraulic impactor results from obtaining a proper ratio of the operating frequency (W) of the tool, to the natural frequency of the oscillation of piston 59 (W,,). (W,,) is the natural frequency of the piston cavity system, when inlet ports 53, 55 are blocked. For satisfactory operation, the range of the ratio of W/W, should lie between 0.55 and 0.95. It has been found that the most practicable operation occurs between 0.70 and 0.80. This range of the ratio of WW, provides sufficient design latitude to obtain desirable physical sizing and operating conditions for pressures, flow, piston mass, cavity volume, piston stroke (both when striking a moil and when not'striking a moil), hydraulic transmission line characteristic impedance, hydraulic transmission line length, and amplitude of alternating flow output at the pump. The ratio for W/ W,, may be calculated as follows:

Where W is the operating frequency of the alternating flow pump in radians per second W,, is the natural frequency of the piston cavity system in radians per second, A is the differential area in square feet of the enlarged portion of piston 59, c is the velocity of sound propagation in the hydraulic fluid in feet per second, M is the mass of piston 59 in slugs, V is the effective volume of one of the fluid cavities, such as cavity 61, in cubic feet (assuming volumes 61 and 63 are the same) and p, is the density of the hydraulic fluid in slugs per cubic foot. If the ratio of W/W is below 0.55, the system will operate erratically and will not deliver power efficiently. At values of W/W higher than 0.95, pressures within the cavities 41, 43 and displacements of piston 39 become higher than is practicable.

In the above described apparatus it is important to keep the length of the hydraulic transmission lines between the alternating flow pump and the hydraulic impactor less than approximately l/60th of a wavelength (as measured by the velocity of sound propagation within the hydraulic fluid contained in the transmission lines). When such transmission lines are greater than l/60th of a wavelength in length, the problem of properly designing the transmission lines coupling the alternating flow pump to the impactor becomes critical and special methods and techniques must be utilized.

. \Nhile the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to changes and modifications without departing from the essence thereof. For example, the pump means 39 may consist of two pumps, one of which produces alternating fluid flow, and the other of which produces direct fluid flow, each such flow being introduced into the appropriate impactor cavity in the proper phase relationship. In its broadest aspect the invention is not limited to the pump means 39 shown and described, but encompasses any pump or combination of pumps capable of producing direct and alternating fluid flows. Also for example, the differential areas of the mass acted on by thefluid in cavities and the cavity volumes may differ between the top and bottom. The geometrical forms of the impactor components may be varied within the broad scope of the invention.

What is claimed is: 1. Hydraulic impactor apparatus comprising: a hydraulic pump having at least two out-of-phase, alternating flow fluid outputs, each output having a direct fluid flow component in addition to an alternating flow component;

power means connected with and motivating said hydraulic pump;

a housing having two cavities, each in communication with a respective fluid output, thus effecting out-of-phase alternating flow into said cavities;

-a piston mounted inrsaid housing between and communicating with said cavities, and having an enlarged mid-region that substantially separates the cavities;

bearing means between the piston and the housing;

a passageway formed through said housing and having its ends terminating at the inner surface of the housing approximately at the extremities of the enlarged end region of the piston;

a discharge port extending through the housing between said passageway and the exterior of the housing; Y

a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.

2. Hydraulic impactor apparatus comprising:

a hydraulic pump having a wobble plate and a plurality of pistons reciprocated by said wobble plate during rotation to provide alternating fluid flow, said pistons being grouped into two banks, each of which connects with a separate fluid output and in addition has at least one piston associated with inlet and outlet check valves to provide a direct fluid flow superimposed on said alternating fluid flow, the output fluid flow of each bank being outof-phase relative to the output fluid flow of the other bank;

power means connected with and motivating said hydraulic pump;

a housing having two cavities each in communication with a respective said fluid output, thus effecting out-of-phase alternating flow into said cavities;

a piston mounted in said housing between and communicating with said cavities, and having an enlarged mid-region that substantially separates the cavities;

bearing means between the piston and the housing;

a passageway formed through said housing and having its ends terminating at the inner surface of the housing approximately at the extremities of the enlarged end region of the piston;

a discharge port extending through the housing between said passageway and the exterior of the housing; and

a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.

3. Hydraulic impactor apparatus comprising: I

a hydraulic pump having at least two out-of-phase, alternating flow fluid outputs, each output having a direct fluid flow component in addition to an alternating flow component;

power means connected with and motivating said hydraulic pump;

a housing having two cavities, each in communication with a respective fluid output, thus effecting out-of-phase alternating flow into said cavities;

a piston mounted in said housing between and communicating with said cavities, and having an enlarged mid-region that substantially separates the cavities through engagement with a central portion of the housing;

bearing means between the piston and the housing;

a passageway formed through said housing and-having its ends terminating at the inner surface of the housing approximately at the extremities of the enlarged end region of the piston;

a discharge port extending through the housing between said passageway and the exterior of the housing;

a flow restriction means mounted in said discharge port to provide a selected minimum fluid pressure to prevent cavitation; and

a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby. v

4. The apparatus of claim 3 in which said flow restriction means comprises an orifice.

5. The apparatus of claim 3 in which said selected minimum fluid pressure is not less than 250 psia to prevent cavitation and to maintain essentially constant fluid acoustic properties.

6. Hydraulic impactor apparatus comprising:

fluid flow generator means for producing a direct fluid flow component and an alternating fluid flow component in two outputs in which the alternating fluid flow components are out-of-phase;

a housing connected with said fluid flow generator means;

a piston with an enlarged portion and end'portions defining differential areas communicating with separated fluid cavities in the housing, each such cavity being connected respectively with one of said out-of-phase outputs;-

piston centering means carried by the housing and including a passageway having the ends terminating at the inner surface of the housing approximately at the extremities of the enlarged portion of the piston, and a discharge port communicating with said passageway to effect a flow passage for the direct fluid flow component from each cavity past one edge region of one end extremity of said enlarged portion of the piston; and

a moil carried by said housing in proximity with said piston for impacting thereby.

7. The apparatus of claim 6 which further comprises a flow restriction means in the discharge port to main- 1 tain a selected minimum fluid pressure to prevent cavitation.

8. The apparatus of claim 7 in which the flow restriction means comprises an orifice.

9. The apparatus of claim .7 in which said flow restriction means is sized to maintain a pressure of at least 250 psia.

10. Hydraulic impactor apparatus comprising:

a hydraulicpump means having at least two out-ofphase, piston generated alternating flow fluid outputs, each output having a piston generated direct fluid flow component in addition to an alternating flow component;

power means connected with and motivating said hydraulic pump;

a housing having two cavities, each of which being in communication with a respective said fluid output, thus effecting out-of-phase alternating flow into said cavities;

a piston mounted in said housing between said cavinicating therewith to reciprocate the piston responsive to' the out-of-phase alternating flow into the cavities;

a discharge port in the housing to discharge the direct fluid flow from the housing;

a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.

11'. The apparatus of claim 10 which further comprises a flow restriction means in said discharge port to provide a selected minimum fluid pressure.

12. The apparatus of claim 11 in which said flow restriction means comprises an orifice.

13. The apparatus of claim 11 in which said selected minimum fluid pressure is not less than 250 psia.

14. Hydraulic impactor apparatus'comprising:

fluid flow generator means for producing a direct flow component and an alternating flow component in two outputs in which the alternating fluid flow components are out-of-phase;

a housing connected with said fluid flow generator means; i

a piston carried by the housing with an enlarged portion and end portions defining differential areas communicating with separated cavities in the housing, said cavities being connected respectively with said out-of-phase outputs, the ratio of the operating frequency of the alternating fluid generator to the natural frequency of the piston cavity system being in a range between 0.55 and 0.95;

a discharge port connected with each said cavity to provide for the discharge of said direct flow components; and

a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby. I

15. The apparatus of claim 14 which further comprises a flow restriction means in the discharge port to maintain a selected minimum fluid pressure.

I6.'The'apparatus of claim 15 in which the flow restriction means comprises an orifice.

17. The apparatus of claim 15 in which said flow restriction means is sized to maintain a pressure of at least 250 psia.

18. The apparatus of claim 14 in which said ratio is between 0.70 and 0.80.

19. The method of hydraulic impacting comprising the steps of:

generating out-of-phase alternating fluid flows in two separated fluid regions;

generating a selected quantity of direct fluid flow in v each said region; transmitting the fluid separate cavities; interposing between said cavities a mass for periodic movements responsive to the out-of-phase fluid flows in said cavities;

discharging from said cavities said selected quantity of fluid while maintaining a selected minimum fluid pressure to prevent cavitation;

impacting a moil with the mass during its periodic movements;

the ratio of the operating frequency to the natural frequency of the piston cavity system being in a range of 0.55 to 0.95 by sizing the system components in accordance with the expression:

flows in said regions to two is the density of the hydraulic fluid in slugs per cubic,

earls; a piston carried by the housing with an enlarged por-v tion and end portions defining differential areas communicating with separated cavities in the housing, said cavities being connected respectively with said out-of-phase outputs;

the ratio of the operating frequency to the natural frequency of the piston cavity system being in a range of 0.55 to 0.95 by sizing the system components in accordance with the expression:

where W is the operating frequency of the alternating flow pump in radians per second, W is the natural frequency of the piston cavity system in radians per second, A is a differential area in square feet of the enlarged portion of the piston, c is the velocity of sound propagation in the hydraulic fluid in feet per second M is the mass of the piston in slugs, V is the effective volume of one of the fluid cavities in cubic feet, and p is the density of the hydraulic fluid in slugs per cubic foot; and

a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.

23. The apparatus of claim 22 which further comprises means maintaining the pressure in said cavities at not less than 250 psia.

24. The apparatus of claim 22 which further comprises piston centering means carried by the housing and in communication with said piston.

25. The apparatus of claim 22 in which the ratio of W/W is between 0.70 and 0.80. 

1. Hydraulic impactor apparatus comprising: a hydraulic pump having at least two out-of-phase, alternating flow fluid outputs, each output having a direct fluid flow component in addition to an alternating flow component; power means connected with and motivating said hydraulic pump; a housing having two cavities, each in communication with a respective fluid output, thus effecting out-of-phase alternating flow into said cavities; a piston mounted in said housing between and communicating with said cavities, and having an enlarged mid-region that substantially separates the cavities; bearing means between the piston and the housing; a passageway formed through said housing and having its ends terminating at the inner surface of the housing approximately at the extremities of the enlarged end region of the piston; a discharge port extending through the housing between said passageway and the exterior of the housing; a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.
 2. Hydraulic impactor apparatus comprising: a hydraulic pump having a wobble plate and a plurality of pistons reciprocated by said wobble plate during rotation to provide alternating fluid flow, said pistons being grouped into two banks, each of which connects with a separate fluid output and in addition has at least one piston associated with inlet and outlet check valves to provide a direct fluid flow superimposed on said alternating fluid flow, the output fluid flow of each bank being out-of-phase relative to the output fluid flow of the other baNk; power means connected with and motivating said hydraulic pump; a housing having two cavities each in communication with a respective said fluid output, thus effecting out-of-phase alternating flow into said cavities; a piston mounted in said housing between and communicating with said cavities, and having an enlarged mid-region that substantially separates the cavities; bearing means between the piston and the housing; a passageway formed through said housing and having its ends terminating at the inner surface of the housing approximately at the extremities of the enlarged end region of the piston; a discharge port extending through the housing between said passageway and the exterior of the housing; and a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.
 3. Hydraulic impactor apparatus comprising: a hydraulic pump having at least two out-of-phase, alternating flow fluid outputs, each output having a direct fluid flow component in addition to an alternating flow component; power means connected with and motivating said hydraulic pump; a housing having two cavities, each in communication with a respective fluid output, thus effecting out-of-phase alternating flow into said cavities; a piston mounted in said housing between and communicating with said cavities, and having an enlarged mid-region that substantially separates the cavities through engagement with a central portion of the housing; bearing means between the piston and the housing; a passageway formed through said housing and having its ends terminating at the inner surface of the housing approximately at the extremities of the enlarged end region of the piston; a discharge port extending through the housing between said passageway and the exterior of the housing; a flow restriction means mounted in said discharge port to provide a selected minimum fluid pressure to prevent cavitation; and a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.
 4. The apparatus of claim 3 in which said flow restriction means comprises an orifice.
 5. The apparatus of claim 3 in which said selected minimum fluid pressure is not less than 250 psia to prevent cavitation and to maintain essentially constant fluid acoustic properties.
 6. Hydraulic impactor apparatus comprising: fluid flow generator means for producing a direct fluid flow component and an alternating fluid flow component in two outputs in which the alternating fluid flow components are out-of-phase; a housing connected with said fluid flow generator means; a piston with an enlarged portion and end portions defining differential areas communicating with separated fluid cavities in the housing, each such cavity being connected respectively with one of said out-of-phase outputs; piston centering means carried by the housing and including a passageway having the ends terminating at the inner surface of the housing approximately at the extremities of the enlarged portion of the piston, and a discharge port communicating with said passageway to effect a flow passage for the direct fluid flow component from each cavity past one edge region of one end extremity of said enlarged portion of the piston; and a moil carried by said housing in proximity with said piston for impacting thereby.
 7. The apparatus of claim 6 which further comprises a flow restriction means in the discharge port to maintain a selected minimum fluid pressure to prevent cavitation.
 8. The apparatus of claim 7 in which the flow restriction means comprises an orifice.
 9. The apparatus of claim 7 in which said flow restriction means is sized to maintain a pressure of at least 250 psia.
 10. Hydraulic impactor apparatus comprising: a hydraulic pump means having at least two out-of-phase, piston generated alternating flow fluid outputs, each output having a piston generatEd direct fluid flow component in addition to an alternating flow component; power means connected with and motivating said hydraulic pump; a housing having two cavities, each of which being in communication with a respective said fluid output, thus effecting out-of-phase alternating flow into said cavities; a piston mounted in said housing between said cavities, and with respective end portions communicating therewith to reciprocate the piston responsive to the out-of-phase alternating flow into the cavities; a discharge port in the housing to discharge the direct fluid flow from the housing; a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.
 11. The apparatus of claim 10 which further comprises a flow restriction means in said discharge port to provide a selected minimum fluid pressure.
 12. The apparatus of claim 11 in which said flow restriction means comprises an orifice.
 13. The apparatus of claim 11 in which said selected minimum fluid pressure is not less than 250 psia.
 14. Hydraulic impactor apparatus comprising: fluid flow generator means for producing a direct flow component and an alternating flow component in two outputs in which the alternating fluid flow components are out-of-phase; a housing connected with said fluid flow generator means; a piston carried by the housing with an enlarged portion and end portions defining differential areas communicating with separated cavities in the housing, said cavities being connected respectively with said out-of-phase outputs, the ratio of the operating frequency of the alternating fluid generator to the natural frequency of the piston cavity system being in a range between 0.55 and 0.95; a discharge port connected with each said cavity to provide for the discharge of said direct flow components; and a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.
 15. The apparatus of claim 14 which further comprises a flow restriction means in the discharge port to maintain a selected minimum fluid pressure.
 16. The apparatus of claim 15 in which the flow restriction means comprises an orifice.
 17. The apparatus of claim 15 in which said flow restriction means is sized to maintain a pressure of at least 250 psia.
 18. The apparatus of claim 14 in which said ratio is between 0.70 and 0.80.
 19. The method of hydraulic impacting comprising the steps of: generating out-of-phase alternating fluid flows in two separated fluid regions; generating a selected quantity of direct fluid flow in each said region; transmitting the fluid flows in said regions to two separate cavities; interposing between said cavities a mass for periodic movements responsive to the out-of-phase fluid flows in said cavities; discharging from said cavities said selected quantity of fluid while maintaining a selected minimum fluid pressure to prevent cavitation; impacting a moil with the mass during its periodic movements; the ratio of the operating frequency to the natural frequency of the piston cavity system being in a range of 0.55 to 0.95 by sizing the system components in accordance with the expression: where W is the operating frequency of the alternating flow pump in radians per second, Wn is the natural frequency of the piston cavity system in radians per second, A is the differential area in square feet of the enlarged portion of the piston, c is the velocity of sound propagation in the hydraulic fluid in feet per second, M is the mass of the piston in slugs, V is the effective volume of one of the fluid cavities in cubic feet, and Rho o is the density of the hydraulic fluid in slugs per cubic feet.
 20. The method of claim 19 in which the selected minimum fluid pressure in said cavities is not less than 250 psia.
 21. The method of claim 19 which further comprises the step of centering mass reciprocation with respect to the housing by controlling the discharge of fluid from each of said cavities.
 22. Hydraulic impactor apparatus comprising: fluid flow generator means for producing a direct flow component and an alternating flow component in two outputs in which the alternating fluid flow components are out-of-phase; a housing connected with said fluid flow generator means; a piston carried by the housing with an enlarged portion and end portions defining differential areas communicating with separated cavities in the housing, said cavities being connected respectively with said out-of-phase outputs; the ratio of the operating frequency to the natural frequency of the piston cavity system being in a range of 0.55 to 0.95 by sizing the system components in accordance with the expression: where W is the operating frequency of the alternating flow pump in radians per second, Wn is the natural frequency of the piston cavity system in radians per second, A is a differential area in square feet of the enlarged portion of the piston, c is the velocity of sound propagation in the hydraulic fluid in feet per second, M is the mass of the piston in slugs, V is the effective volume of one of the fluid cavities in cubic feet, and Rho o is the density of the hydraulic fluid in slugs per cubic foot; and a moil supported by the housing in proximity with one end of the piston for periodic impacting thereby.
 23. The apparatus of claim 22 which further comprises means maintaining the pressure in said cavities at not less than 250 psia.
 24. The apparatus of claim 22 which further comprises piston centering means carried by the housing and in communication with said piston.
 25. The apparatus of claim 22 in which the ratio of W/Wn is between 0.70 and 0.80. 